Extensible assembly



Patented Aug. 1, 1944 UNITED STATES PATENT OFFICE 4 Claims.

This invention relates to extensible assemblies such as comprise elongate sections adapted to be telescoped one within the other and to be extended from telescoped position to form a pole or other elongate article. Familiar examples of such assemblies are radio antennae masts made of assemblies of metal tubing, or of elongate sections of other shape, so arranged that at least some of the sections telescope when not in use and when in use extend outwardly of each other except for an overlap of their adjacent extremities, which overlap forms a joint between adjacent sections. Such joints must be readily made, or broken, as the mast is raised or lowered, and when formed must be strong enough to resist bendingloads caused by forces acting at right angles to the axis of the mast. In joints of this character as were used prior to this invention,

it is customary to provide for contact between the inner surface of the outside tube and the outer surface of the inside tube throughout the axial length of the overlap Or in bands extending longitudinally of the overlap. The strength and rigidity of the joint so formed is dependent upon the axial length of this overlapping relationship and in many instances the surfaces engaged in the overlapped joint become deformed or accumulate dirt or other foreign matter, and the joint is made and broken only with difficulty. Moreover, the contacting surfaces in the joint must be accurately sized or machined to giv a close sliding fit over the entire distance of the overlap.

The object of the present invention is to provide extensible assemblies, such as above described, in which adjacent sections form, in extended positions, overlapping joints of the reouired axial length but without contact between the overlapping surfaces over the entire axial length of the overlap, thus decreasing the extent of surface which must be free of deformation or of the presence of foreign matter or which must be accurately sized to insure a closely fitting joint.

Although, as will be apparent from the following description, extensible assemblies of the character described may be used for many purposes and the extensible sections thereof may take many forms, the invention will be explained with reference to a radio mast built of simple tubular Sections. In the drawing, in which like numerals designate like parts;

Fig. 1 is an elevational view of a portion of such a mast, and

Fig. 2 is an enlarged sectional view taken longitudinally through the mast shown in Fig. 1.

As shown in the drawing, the mast consists of the tubular sections l, 2 and 3. It may be assumed for the purposes of this description that section I and section 3 are end sections although it will be apparent that either of these sections might, like section 2, lie intermediate of other sections. Section I of the mast assembly is larger than the remaining sections, as each succeeding section is larger than the preceding section, thus allowing, if desired, complete telescoping of all of the sections into the length of one section. The end of the larger of two adjacent sections is provided at the extremity at which it overlaps the extremity of the adjacent smaller section, with an inner surface converging in steps 5 toward th orifice through which the elongated body of the smaller section operates. As here shown, these steps 5 form on the innersurface of the tube a socket consisting of a series of axially aligned bores or cavities, the bores of smaller cross sectional area being adjacent the tube orifice. The smaller tube, 1. e. section 2 or section 3, is provided with an enlarged end portion which converges outwardly in steps 4 to the end of the tub to form a series of axially aligned surfaces having the same geometric form as the axially aligned bores of the socket formed on the inner surface of the larger tube. Each of these surfaces of the enlarged end portions is so sized as to slidably engage the surfaces of a socket bore of similar size as the smaller tube is drawn forward out of its telescoped postlon to the extended position shown in the drawing. In the form of the invention shown in the drawing, a stop 1 is provided on the larger tube at its orifice to prevent further movement of the parts at a prede; termined point. The axial distance between the steps 5 on the larger tube and the axial distance between the steps 4 on the enlarged end of the smaller tube are so adjusted with respect to each other and to th stop 1 that when the joint is complete the contact between the surfaces of the enlarged end portion of the extending member and the walls of the socket formed in the larger tube is limited to a plurality of longitudinally spaced bandular areas, indicated by the stippled areas on Fig. 2, surrounding the axis of the mast. In the length of the overlap joint between said bandular areas contact between the overlapping surfaces does not take place, thus eliminating the evils of a long bearing surface without decreasing the effective length of the overlap or, consequently, the strength and rigidity of the joint. While in the simple structure here shown only two such bands of contact are provided, it will be apparent that by increasing the number. of steps 5 on the inner surfac of the larger tube and the number of steps 4 on the enlarged end of the extending member (section 2 or section 3) the number of bandular areas may be multiplied. It is likewise contemplated that the shape of the socket cavities or bores formed by the steps 5 on the inner surface of the outer tube may be that of a round cylinder or may be of other shape simple in geometric cross section, such as an oval, an octagon, etc., in which case the end of the inner tube designed to fit in the socket would correspond thereto in geometric shape. It is likewise contemplated that the means for limiting the distance which the enlarged end portion of an extensible member travels into the socket of the outer member or tube may be varied from that shown, it only being necessary that the contacts between the cavity surfaces and the corresponding surfaces on the enlarged end portion be restricted to longitudinally spaced bandular areas. When there are but two of such bandular areas they should preferably be located at opposite extremities of the overlap, as shown in Fig. 2. In the preferred forms of my invention the total area of contact between the overlapping extremities of the members is as small as possible and a good example of the relation of the total area of contact to the total area of overlap is illustrated, approximately to scale, in Fig. 2. In any event, I prefer that the total area of contact be less than one-half the total area of the efiective joint overlap (in Fig. 2 it is shown as approximately 5 but benefits will be obtained whenever the area of contact between the overlapping surfaces is materially reduced so longv as it is largely restricted to the bandular areas described.

when the members of the extensible assembly are composed of materials, such as some kinds of wood, not suited to form engaging surfaces, or when the members are so made that step-like surfaces are not readily formed thereon, or wherever convenience dictates, the socket portion cavity of the receiving larger member and the engaging surfaces of the enlarged end portion of the extending member, or either, may be fashioned of other materials or take the form of fixtures mechanically or otherwise attached to the members.

In many cases it is not advisable to so fashion the contacting surfaces of the joint that the engagement therebetween is too tight, in which cases holding members may be inserted through the overlapped portions to hold the members in extended position. Such holding members may conveniently take the form of the pins 8 shown in ig. 2.

Having thus described my invention and illustrated a preferred form thereof, I claim:

1. In an extensible assembly including a section adapted to telescope within another section and to be extended therefrom to form an extended article with adjacent end portions of the sections lapped in slidable engagement, an extensible member having an elongate body portion one end of which is enlarged in steps disposed at longitudinal intervals to form a series of surfaces defining similarly shaped portions of sucsurrounding the axis of the extensible member and spaced longitudinally thereof to provide areas between said band-like areas in which said surfaces and walls are not in contact.

2. An extensible assembly comprising a tube the inner diameter of which is decreased, at one end of the tube, in steps to form a socket composed of a series of concentric bores the smallest of which is adjacent the tube orifice, an extensible member adapted to be received within said tube and comprising" an elongate body portion sized to operate through said orifice to form an extension of the tube, said member being provided with an enlarged end composed of a series of axially aligned cylinders of successively smaller diameter the smallest of which is adjacent said body portion, said cylinders being sized to be received with said socket with theirsurfaces the enlarged end is limited to a series of longicessively increased size, a tube-like member having an axial cavity to receive said extendingmember, 'said cavity terminating in an orifice through which the said elongate body portion of tudinally spaced circumferential areas of differing diameters.

3. In an assembly, a tube, an elongate extending member adapted to be positioned within the tube and to move outwardly therefrom through an orifice thereof to form an extended article, and means for forming an overlapped joint between adjacent extremities of the tube and th extending member when the assembly is extended, said means comprising an enlarged end on the extending member adapted to be received in a socket contained in said tube adjacent said orifice and to slidably engage the walls of said socket as said member moves outwardly into extended position, the engaging surfaces of the end being stepped downwardly at intervals toward the elongate body of the extending member, the socket having surface engaging walls stepped downwardly at intervals toward said tube orifice, and the distance between steps on the end portion and the distance between steps on the socket-being predetermined so that at least one of the said engaging surfaces will engage only a portion of a corresponding socket wall when outward movement of the extending member is complete.

4. An extensible body comprising an outer tube the inner walls of which converge in steps at one end thereof to form a series of concentric bores the smallest of which is adjacent the tube or orifice and has an axial length less than that of other bores, an inner tube sized to translate in and out of said outer tube through said orifice and having an elongate body section sized to pass in and out of 'said orifice and an end portion larger than said orifice, said end portion converging by steps from its end to the elongate body of said inner tube to form a series of concentric cylindrical surfaces of consecutively lesser diameter and of like number and substantially like diameter to the said concentric bores of the outer tube, the axial length of the concentric cylindrical surfaces being so proportioned that when the entire axial length of the smallest bore is frictionally engaged by the cylindrical surface of corresponding diameter the engagement of other cylindricalsurfaces on said end portions will be limited to an axial distance equal to th axial length of said smallest bore. 1

BOYNTON J. FLETCHER. 

